Recently, a contactless communication medium using short-range wireless communication is used to transmit and receive information in an automatic ticket checking system, an information card system and so on. In the contactless communication medium, for example, communication and storage of identification number, identification information, value information, credit information or the like are performed. The contactless communication medium includes, for example, a data carrier, and a card-type contactless IC card attached to people, vehicles or goods so as to be used. There is wireless communication based on a near-field communication (NFC) scheme using 13.56 MHz as a carrier frequency as a type of short-range wireless communication.
In the short-range wireless communication, for example, a Qi scheme using a frequency of 100 to 200 KHz, a wireless power consortium (A4WP) scheme using a frequency of 6.78 MHz, and the like have been known in addition to the NFC scheme. Further, A4WP and a power matters alliance (PMA) were merged in November 2015 under a new title of “Air Fuel Alliance” and a wireless scheme thereof is “Air Fuel.”
In wireless power feeding, for example, the following two schemes have been well known. A first wireless power feeding scheme is a magnetic resonance scheme. In the magnetic resonance scheme, a power transmission side resonance circuit including a power transmission side coil is used in a power feeder, and a power reception side resonant circuit including a power reception side coil is used in a power receiver. The resonance frequencies of the power transmission side resonance circuit and the power reception side resonance circuit are set at a common predetermined frequency. A magnetic field is generated in the power transmission side coil by allowing an AC current to flow through the power transmission side coil. This magnetic field causes an AC current to flow through the power reception side coil. That is, electric power is supplied from the power transmission side resonance circuit including the power transmission side coil to the power reception side resonance circuit including the power reception side coil. The magnetic resonance scheme is employed as, for example, an A4WP scheme.
A second wireless power feeding scheme is an electromagnetic inductive scheme. In the electromagnetic inductive scheme, two coils are arranged close to each other and a magnetic flux generated by allowing a current to flow through one coil is coupled to the other coil to generate power energy in the other coil. As the electromagnetic inductive scheme, for example, a Qi scheme, a PMA scheme, and an NFC scheme have been well known.
Recently, a contactless communication medium compatible for both the magnetic resonance scheme and the electromagnetic inductive scheme has also been introduced.
A contactless type information card and IC using a magnetic resonance scheme is disclosed in the related art. In the contactless type information card and IC, a parallel resonance circuit is configured by a loop antenna, a condenser, and a variable capacitance element. When the contactless type information card and the loop antenna of a reader/writer of the IC are very close to each other, the power energy received by the contactless type information card and the loop antenna of the IC increases. In this case, a voltage applied to the variable capacitance element changes and a capacitance value of the variable capacitance element changes. Thus, the resonance frequency is shifted depending on the received voltage and the reception efficiency is lowered. As a result, the received voltage is prevented from being excessive.
A power reception device, a power transmission device, and a contactless power feeding system using a magnetic resonance scheme are disclosed in the related art. The power reception device is a circuit connected to a reception side resonance circuit including a power reception side coil and a power reception side capacitance, and includes a power reception circuit for generating an output electric power depending on electric power received by the power reception side coil using magnetic resonance. In addition, the power reception device includes a change/short circuit for changing a resonance frequency of the power reception side resonance circuit from a reference frequency or short-circuiting the power reception side coil before receiving electric power. In the related art, it is described that, in a state in which a foreign object is disposed on a power feeding stand, the foreign object is destroyed by a strong magnetic field generated by the power transmission side coil, and it is suggested that a terminal voltage of a coil of the foreign object on the power feeding stand increases, for example, from 100 to 200V. In some instances, the magnetic field strength generated in the power transmission side coil is, for example, about 45 to 60 A/m, and this magnitude is greater than a magnetic field strength of 7.5 A/m which is an upper limit value defined by the NFC standard. Further, in the related art, a circuit for changing a resonance frequency and a circuit for short-circuiting a reception side coil are disclosed respectively.
A semiconductor IC device and a contactless type IC card using a magnetic resonance scheme are disclosed in the related art. This semiconductor IC device includes a reception circuit for demodulating an information signal received via an antenna. The reception circuit includes an antenna terminal connected to the antenna and a rectifying circuit for rectifying and smoothing an AC signal applied to the antenna terminal. The contactless type IC card is equipped with a coil constituting the antenna, an input/output terminal provided on the surface of the IC card, and the IC device connected to the coil.
An electromagnetic inductive coupling device using an electromagnetic inductive scheme different from the magnetic resonance scheme is disclosed in the related art. The electromagnetic inductive coupling device disclosed in the related art includes an electromagnetically induced coil, a rectifying circuit for full-wave reflecting power energy taken through the coil, and a smoothing circuit for smoothing an output from the rectifying circuit to generate a predetermined internal power. In addition, the electromagnetic inductive coupling device includes a MOS transistor which is connected in parallel between both ends of the coil and operates in response to an output from the smoothing circuit.
An “extended specification” necessary for securing compatibility by reflecting the verification result of a contactless IC card that conforms to the ISO/IEC14443 is disclosed in the related art. The physical and electrical properties of a proximity IC card (PICC) and a proximity coupling device (PCD), and their antenna shapes, resonance frequencies, generated magnetic fields and the like are disclosed in the related art. For example, the resonance frequency of the PICC is proposed to be 13.56 MHz or more. In addition, “testing of PCD to be tested” is described and it is proposed that a reception voltage of a maximally generated magnetic field is 3V or less in an operating range of the PCD.
In a case where wireless power feeding is performed between the power feeder and the power receiver, a strong magnetic field is generated around the power feeder regardless of whether the magnetic resonance scheme or the electromagnetic inductive scheme is used. When the contactless communication medium approaches the power feeder and is exposed to the strong magnetic field, a high voltage is generated in the internal circuit of the contactless communication medium by the resonance circuit and the like within the contactless communication medium. Due to this high voltage, the internal circuit of the contactless communication medium may be damaged.
A technique of stopping power feeding when a medium, a foreign object or the like that does not respond to such wireless power feeding accidentally approaches the power feeder has been proposed. However, since it is also considered that the contactless communication medium approaches a power feeder that does not employ such a technique, it is desirable to install a voltage protection circuit in the contactless communication medium itself.
The contactless type information card and IC are limited to those that are supplied with electric power for driving the internal circuit by electromagnetic waves emitted from a communication destination device and perform data communication with the communication destination device in the related art. Thus, the scope to which the corresponding disclosure is applied is limited to the one in which the contactless type information card and IC and the communication destination device are systematically integrated. In other words, the overvoltage protection disclosed in the related art cannot be expected for general cards such as an RFID card, an NFC card, and the like.
In another related art, it is intended to control or stop the operation of the resonance circuit of the power reception side but does not consider a countermeasure such as damage prevention or the like in the information card itself. Thus, there is a possibility that the information card itself is deteriorated or enters a state in which it cannot withstand being used before the resonance circuit of the power reception side is stopped.
In another related art, it is intended to protect the reception side device, and protection of an information card is not disclosed. Thus, like the above-mentioned related art, there is a possibility that various kinds of information retained in the information card are deteriorated or enter a state in which they cannot withstand to be used before the power reception side device is protected.
In another related art, it is admitted to suggest that an AC power itself applied to the rectifying circuit is limited using the MOS transistor connected in parallel to the coil that receives an output from the smoothing circuit. However, since a specific size of an output of the smoothing circuit or a specific magnitude of a magnetic field is not disclosed, it cannot be expected for practical application.
The above-mentioned related arts are common in that they have means for attenuating sensitivity of a magnetic field when the magnetic field is strong. However, it is uncertain whether such means for attenuating sensitivity of the magnetic field is adapted to the magnetic field strength defined by the ISO/IEC14443. Thus, even though attenuation means operates, there is a possibility that an operating point of the attenuation means greatly exceeds the magnetic field defined by the ISO/IEC14443 or operates in magnetic field strength weaker than a predetermined magnetic field strength.